Skeletal muscle atrophy that occurs during disuse is linked to poor functional and metabolic health outcomes. Small noncoding microRNAs (miRNAs) are now appreciated as important components in the regulation of muscle growth and atrophy and can be carried through systemic circulation in exosomes to potentially mediate systemic adaptations. However, little is known about how atrophic conditions influence the miRNA content of exosomes. The purpose of this study was to determine changes in exosome miRNA in response to atrophic conditions. Adult (10 months old) Brown Norway/F344 male rats were subjected to either normal, weight‐bearing conditions (WB: n=7) or a 7‐day hindlimb suspension (HS: n=6) protocol that is known to induce significant skeletal muscle atrophy in select hindlimb muscles. Rats received deuterium oxide (D2O) over 10 days to label newly synthesized proteins for determination of fractional synthesis rate (FSR, %/day). Rat serum was collected and filtered through a 0.22μm filter for removal of larger extracellular vesicles. Exosomes were isolated using the ExoQuick™ Precipitation solution before isolation of the exosome miRNA. As expected, HS had lower myofibrillar skeletal muscle FSR compared with WB rats (0.72 ± 0.09%/day vs 1.64 ± 0.27%/day; p<0.05). MiRNA microarray analysis of exosome miRNA revealed 73 differentially expressed (p<0.05) miRNA between WB and HS conditions. The list of differentially expressed exosome miRNAs was uploaded to DIANA‐miRPath for pathway analysis and prediction of regulatory pathways potentially impacted by the altered exosome miRNAs during atrophy. Various pathways related to muscle protein homeostasis were significantly predicted (p<0.01) to be targeted by the differentially expressed exosome miRNA, including MAPK signaling, focal adhesion, Rap1 signaling, FOXO signaling, ubiquitin mediate proteolysis, TGF‐beta, and mTOR signaling. These data suggest that alterations in systemic exosome miRNA reflect changes in the major pathways dictating muscle atrophy during muscle disuse. In addition, selective packaging and release of exosomes containing miRNA important for regulation of muscle atrophy may be a major contributor to determining skeletal muscle homeostasis during muscle disuse.Support or Funding InformationNIH grants AT009268 and AG042699This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.